High efficiency secondary and back scattered electron detector

Abstract

An assembly for a charged particle detection unit is described. The assembly comprises a scintillator disc, a partially coated light guide a thin metal tube for allowing the primary charged particle beam to pass through and a photomultiplier tube (PMT). The shape of scintillator disc and light guide are redesigned to improved the light signal transmission thereafter enhance the light collection efficiency. A light guide with a conicoidal surface over an embedded scintillator improved the light collection efficiency of 34% over a conventional design.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]Not ApplicableSTATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT[0002]Not ApplicableREFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK[0003]Not ApplicableFIELD OF THE INVENTION[0004]The present invention relates to a charged particle detection device, more specifically, to a detection device that detecting backscattered electrons and secondary electrons emanating from substrate surface after being impinged by a charged particle beam.BACKGROUND OF THE INVENTION[0005]A charged particle detector is an indispensable part of a charged particle (ion or electron beam) instruments, for example, a scanning electron microscope (SEM). In a SEM, an electron beam emanated from an electron source is focused into a fine probe over a specimen surface and scanned by a deflection unit in a raster fashion; and signal electrons released from the specimen, i...

AI Technical Summary

Benefits of technology

[0017]A detection device for detecting backscattered electrons and secondary electrons induced by impinging charged particle beam comprising a scintillator disc, a light guide, a thin metal tube and a PMT; wherein the light guide with a conicoidal surface is cohered over the top of the scintillator disc and the light guide is cohered with or is mechanically attached to the PMT. The advantages of the detection device are: 1. the conicoidal portion of the light guide surface with reflective coating improves light collection efficiency by 10%; 2. the truncated-cone type scintillator disc improves light collection efficiency by 16%; 3. the embedded scintillator disc improves light collection efficiency by 23%; 4. the embedded truncated-cone type scintillator disc improves light collection efficiency by 25%; 5. the thin metal tube that made of a high permeability material to permit charged particle passing through can avoid stray electromagnetic field on the scintillator disc to affect passing primary beam.

[0018]In one embodiment the invention, the light collection efficiency is improved by shaping the surface of light guide over the top of the scintillator disc to a conicoidal type surface. Both the light guide and scintillator disc have a through hole to set the thin metal tube through which the primary charged particle beam passing through. On scintillator disc, the opening is located on the center; on light guide, the through hole is located between the vertex and one focus of the conicoid. The conicoidal surface of the light guide is coated with aluminum to improve internal light reflection. The surface of scintillator disc that endure electron impinging is also coated with aluminum to avoid charging effect.

[0019]In another embodiment the invention, further improvement of the light collection efficiency is achieved by shaping the scintillator disc into an upside-down truncated-cone with a slant angle larger than the critical angle of reflection between the scintillate material and vacuum interface beside the light guide with a conicoidal type surface over the top of the scintillator disc. Both the light guide and scintillator disc have a through hole to set the thin metal tube through which the primary charged particle beam passing through. On scintillator disc, the opening is located on the center; on light guide, the through hole is located between the vertex and one focus of the conicoid. The conicoidal surface of the light guide is coated with aluminum to improve internal light reflection. The surface of scintillator disc that endure electron impinging is also coated with aluminum to avoid charging effect.

[0020]In yet another embodiment the invention, the light collection efficiency improvement is achieved by embed a scintillator disc into a light guide with a conicoidal type surface over the top of the scintillator disc. The scintillator disc is manufactured to be cylindrical type. Both the light guide and scintillator disc have a through hole to set the thin metal tube through which the primary charged particle beam passing through. On scintillator disc, the opening is located on the center; on light guide, the through hole is located between the vertex and one focus of the conicoid. The conicoidal surface of the light guide is coated with aluminum to improve internal light reflection. The surface of scintillator disc that endure electron impinging is also coated with aluminum to avoid charging effect.

[0021]In yet another embodiment the invention, further improvement of the light collection efficiency is achieved by shaping the embedded scintillator disc into a truncated-cone with a slant angle smaller than the critical angle of reflection between the scintillate material and light guide interface beside the light guide with a conicoidal type surface over the top of the scintillator disc. Both the light guide and scintillator disc have a through hole to set the thin metal tube through which the primary charged particle beam passing through. On scintillator disc, the opening is located on the center; on light guide, the through hole is located between the vertex and one focus of the conicoid. The conicoidal surface of the light guide is coated with aluminum to improve internal light reflection. The surface of scintillator disc that endure electron impinging is also coated with aluminum to avoid charging effect.

Problems solved by technology

In a conventional design, the electrons to light signal conversion efficiency and light signal collection are low.

In order to compose an image with enough brightness and contrast, a large magnification PMT or magnifying circuit is needed, which will introduce a larger electric noise into the image.

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